Electrical musical instruments



April 25, 1967 R. H. PETERSON ELECTRICAL MUSICAL INSTRUMENTS 3 Sheets-Sheet 1 Filed NOV. 29, 1963 April 25, 1957 Ra H. PETEHSQN 3,316,341

ELECTRICAL MUS ICAL INSTRUMENTS Filed Nov. 29, 1963 3 Sheets-Sheet 2 2@UTPUT OUTPU T SINE CURVE SYNTHESIS OSQOCAN @5 prri 25, w? Eg. N. EETENSQN 3593323@ ELECTRI CAL MUS ICM; INSTRUMENTS Filed Nov. 29, 1963 5 SheeLS-Sheet 3 7 INSTRUMENT PRE AMP AMPUFY //Q\ ,2W 5/2/ N EG.' C FEEDBACK i P6SM l FEEDBACK JWM@ Y United States Patent C) York Filed Nov. 29, 1963, Ser. No. 326,869 5 Claims. (Cl. 84-1.24)

My invention relates to electrical musical instruments, and particularly to novel means for producing desirable tonal effects, incl-uding certain effects not previously associated with such instruments. While primarily applicable to polyphonic musical instruments, certain features of the invention may also be applied to instruments of the monophonic or solo type.

It is convenient to identify the three common systems for producing audio-frequency signal of any particular desired wave shape, which wave shape determines the timbre of the sound wave into which said signal may be translated, as follows:

Harmonic synthesis is by superimposing a series of harmonically related signals. Wave distortion, or shaping, operates by starting with a sine curve and modifying its shape to introduce harmonics. US. Patent 2,649,006 discloses one typical example of this. Formant instruments start with a pulse wave shape, for example a sawtooth, and use various filters to attenuate or emphasize desired harmonic frequencies.

The invention is substantially equally applicable to all three systems. When suitably adapted to any one of the systems, it provides in each instance for dynamic control by the player of changes in the timbre or frequency or amplitude of the processed signal, or of any two or all three of these main characteristics.

The word dynamic is used to identify changes that are not step by step, but smooth and even and without abrupt discontinuities. Abrupt changes result readily from depressing different playing keys in an ordinary musical instrument, and also from the adjustive manipulation of the conventional stops. A good example of a dynamic control is the use of a mute =by a trumpet player. By a continuous physical movement of the mute, he can change the resonance peaks of his instrument, and marked changes in tone quality may be introduced and eliminated at various time rates, lbut always smoothly and without any step 'by step discontinuities, and at the momentary fancy of the player. In electrical musical instruments, this has always been possible with the usual swell pedal, but only with respect to loudness of the entire instrument. Automatic tremulants of a substantial variety have also been successful. But changes in timbre as fully and freely and smoothly variable as in the muting of a horn, have not heretofore been available in electrical musical instruments, so far as I am aware.

The timbre modulations produced according to the invention include two distinct varieties. First, the deviation may correspond at ea-ch instant to the amount of the displacement of a dynamically movable control element activated by the player, so that the time envelope of the modulation is an instantaneous and simultaneous function of the players physical movement. This variety may conveniently be identified as a modulation with a player-controlled envelope.

Second, the envelope may be automatically controlled, as a portamento or a recurring modulation, or a single regular or irregular modulation; but the occurrence of the automatic action may `be conditioned on something done -by the player. This variety can conveniently be identified as a modulation with automatic envelope control, and it may or may not be automatically repetitive.

Among the specific objects of the invention are:

3,316,341 Patented Apr. 25, 1967 ice (l) To provide a variable resonant reed stop for an electrical musical instrument;

(2) To provide means for electrical musical instruments forv enabling the performer to duplicate certain effects ordinarily associated with an orchestra or with `orchestral instruments;

(3) To provide means for the organist to introduce a novel type of expression into the music and thereby render a more truly artistic performance;

(4) To provide novel means for introducing dynamic variations in the tone quality of an electrical musical instrument;

(5) To provide means for quickly altering the tone quality of an electrical musical instrument over a wide range without employing the usual stops, combination action or the like.

Other objects and advantages of the invention will become apparent as the description proceeds.

In the accompaning drawings:

FIGURE 1 is a block diagram indicating the incorporation of the invention in an organ system of the formant type;

FIGURE 2 is a block diagram of an alternative arrangement for formant type instruments;

FIGURE 3 is a schematic circuit diagram indicating one type of filter control suitable for use in the invention;

FIGURE 4 is a schematic circuit diagram of a preferred dynamic filter circuit;

FIGURE 5 is a partial schematic diagram indicating the application of the invention to an organ of the harmonic synthesis type;

FIGURE 6 is a schematic circuit diagram for a triggered, automatically variable, dynamic filter;

FIGURE 7 is a circuit diagram of a dynamic variable filter arranged to produce reiterating effects a-utomatically; and

FIGURE 8 is a block diagram of one 'way of combining the invention as an adjunct to an organ already 1n use.

Referring first to FIGURES 1 and 2, the signal generator has a terminal 102 for delivering the complete composite signal, including superposed signals from the Variety of sources selected at the moment by the player by means of the keys 95, which are representative of the keys of an organ or of one manual of a multi-manual organ. In FIGURE 1, this output enters two parallel channels. At the terminal 104, it enters the regular stop equipment 106 for continuously delivering various timbres by the setting of the conventional stops by the player.

In addition, if the stop switch 108 is closed, the same signal is delivered at terminal 110 to a dynamic filter 112 to be described in detail hereinafter. The signals from the regular stop unit 106 and from the dynamic filter 112 are merged and the combined signal goes to the preamplifier 114 and the loud speaker 115. The conventional swell pedal 101 controls the preamplifier 114. The operators dynamic control of the functioning of the filter 112 is by means of a control lever 118 projecting forward below the keyboard on the console in a position to lie close beside the right knee of the player. The leg control lever 118 is held resiliently in the full line position, but yields readily to be pushed over -by the players knee approximately to the position indicated in the same figure in dotted lines, and the extent of the modification of the signal received by the dynamic filter will vary as a direct, but not necessarily a linear, function of the extent of displacement of the lever.

In FIGURE 2, I have indicated the same generator 100 and regular stop 106; but the dynamic filter 120 is connected in series between the st-Ops 106 and the preamplifier 114. This part of the system of FIGURE 2 performs substantially the identical function of the dynamic filter 112 but because it processes signal that has already been acted on by the regular stops 106, its detail design may be slightly altered for best results. In the system of FIGURE 2, the operator can still play with the regular stops only by closing the by-pass switch 122 so that the signal proceeds from the regular stops to the preamplifier without passing through the filter 120.

One type of dynamic filter adapted for use in the combination of FIGURES 1 and 2 is the resonant or band pass type filter indicated in FIGURE 3. Signal of any frequency appearing across input terminal 110 and ground will arrive at the output terminal 130 with the degree of attenuation a function of frequency. At the resonant frequency of the tuned circuit 132, comprising the capacitor 134 and the inductor 136, the attenuation will be relatively slight, and at frequencies much above or below this resonant frequency the attenuation is greatly increased.

Means are provided for varying the resonant frequency of the tuned circuit 132. I have indicated a magnetic core 138 moveable with respect to the position of coil 136 to vary the value of the inductance. This may be rotated about a pivot 139 by the knee lever 118 projecting out beside the player. The full line position obtains when the lever 118 is not displaced by the operators knee; and movement may proceed to the dotted line position, where the frequency of resonance has been changed greatly.

It will be obvious that signal may .be taken either from terminal 130 or from terminal 140 on the tuned circuit 132.

The sharpness of the resonance peak is a function of the circuit design, including the impedances of the input and output circuits, series resistors 141 and 142, and the components comprising the resonant circuit 132.

As a practical matter, it has been found that because of the relatively large amount of energy represented by the lower frequency c-omponents of a composite organ signal, the actual volume of signal delivered to the output terminal 130 diminishes as the resonant frequency of the tuned circuit is increased. Means are provided for compensating for this undesirable reduction in signal and loudness as the control is moved to or in the direction of higher frequencies. One suitable compensating means is a light-sensitive resistor 146 connected in shunt around resistor 142. A variable density shutter 148 is pivoted on an axis at 150 and moves back and forth between the light source 152 and the light-sensitive resistor 146. A drag link 154 connects the shutter 148 mechanically with the core 138 of the tuned circuit; and as the core moves to the left, the shutter 148 delivers increasing illumination to the light sensitive resistor 146. The resulting decreased resistance increases the energy transmitted through the filter.

Many desirable tonal effects are possible with a dynamic filter according to FIGURE 3, but as a practical matter, it has been found difficult to provide a variable inductor of reasonably constant Q over the very wide range of inductance that has been found to be desirable. Saturable reactors can be used, but the difficulty in obtaining the desired range of inductance in that way without distortion involves complex control apparatus and is not generally desirable.

The resonant or band-pass circuit indicated in FIGURE 4 is tunable over a range of several octaves with relatively constant Q.

As in the circuit of FIGURE 3, the input is supplied across terminal 110 and g-round and the output across ground and terminal 160. Again, the attenuation of signals through the filter is minimum at the resonant frequency of the tuned circuit, which in this case consists of the inductor 162 and the capacitor 164. Instead of being returned directly to ground, capacitor 164 is connected to the emitter of the transistor 166 which is a common collector transistor amplifier having the load resistor 168.

The collector 170 of transistor 166 is connected to a suitable source 167 of supply potential, such as minus ten volts. Resistors 172 and 174 provide bias in the usual manner. Resistor 168, connected between the emitter and ground, is of a 4relatively low value and is ordinarily sufficiently low so that it has a negligible effect upon the circulating current in the resonant circuit 162 and 164. Thus it is seen that with no input signal applied to the base of transistor 166 the filter circuit shown in FIGURE 4 operates in an identical manner to that of the filter in FIGURE 3, with the resonant frequency determined by the values of inductor 162 and capacitor 164. However, if the signal appearing at 176 is applied to the base of transistor 166 through the coupling capacitor 178 and through the resistor 180 (when short circuited) a voltage will now appear at the emitter of transistor 166 that is substantially the same as the voltage appearing at terminal 176. This is because the common collector-amplifier circuit has a gain of approximately unity and produces an output signal across the load resistor 168 that is in phase with the input signal. Since the capacitor 164 now has an identical voltage at both of its terminals, substantially no current can fiow through capacitor 164. As a result, this capacitor has been effectively removed from the resonant circuit and the .resonant frequency of the tuned circuit is now determined primarily by the inductance of inductor 162 and by the distributed capacitance across its winding. The highest frequency to which the resonant circuit 162 and 164 can be tuned is determined by the distributed capacitance of the coil 162, conventionally indicated in FIGURE 4 in dotted lines at 163. Capacitor 164 usually has a value of the order of fifty times the capacitance 163, which allows a range of .resonant frequencies of more than five octaves.

Now by connecting the control element 118 to the variable resistance element 180 it is possible to render the capacitor 164 effective in the resonant circuit to any desired degree by simply adjusting the position of the lever 118. It is interesting to note that in this circuit, the change in the resonant frequency of the tuned circuit is accomplished without substantially affecting the Q of the resonant circuit.

Referring now to FIGURE 5, similar effects may be obtained in organs of the harmonic synthesis type. Organs of this type use tone generators that ordinarily provide pure sinusoidal wave forms and the various organ tone colors are obtained by -combining sine Wave signals that are simultaneously derived from a plurality of harmonically related signal sources. The electric organ system 184 of the tone synthesis type has a plurality of output terminals 177, 179, 181, 183, 185, 187, and 189 adapted to deliver the fundamental, and second, third, fourth, fifth, sixth, and eighth harmonics. It should be understood that in such a system whenever a given key is depressed on the organ keyboard, the plurality of harmonically related signals will all appear respectively at the aforementioned output terminals. When a plurality of keys are depressed, terminal 177 has a composite signal including the fundamentals of all the notes being played; terminal 179 has `the octaves, terminal 181 the third harmonies and so on.

Each harmonic component signal is delivered to a circuit having a light-sensitive resistor in series with an adjustable resistor, which latter can be adjusted by the operator in advance of playing, to determine the selected relative amplitude of each harmonic component. Light-sensitive resistor 191 receives the fundamental, and resistors 192, 193, 194, 195, 196, and 198 the higher harmonics. Conventional means are provided by means of which the player can adjust the relative amplitudes of the different harmonics. These are diagrammatically indicated in FIGURE 5 as variable resistors 200.

A light shutter 202, of variable density, lies in front of the light-sensitive resistors, pivoted at 204 and vrotatable by the knee lever 118. In the usual configuration, sufficient light reaches all the resistors 191, etc. so that some signal will be transmitted, but one or two or three adjacent resistors receive greater illumination and those harmonies are emphasized to determine the timbre of the note produced. Light from the source 206 will reach the resistors 191 etc. in the proportions desired and determined bythe shutter characteristics, and movement of the knee lever 118 will produce the desired shift in the emphasized harmonics as 4the lever is displaced.

The dynamic change can also be produced with an automatically determined time envelope Whenever a predetermined time-change cycle is desired, instead of a variation that is dictated by the players momentary fancy. For instance, a conspicuous timbre change at the inception of each note is a popular feature in certain types of music.

In FIGURE 6, I have indicated a source 250 of negative potential connected t-o bus 252. Three of the playing keys are indicated at 254, 256, and 258. Each key is connected to a trigger bus 260, by a switch 262, with a resistor 264 between the buses 252 and 260. Closure of any one key will deliver potential to the terminal 266 of capacitor 268, equal to the fraction of B-potential, represented by the resistance of resistor 270 between terminal 266 and ground, divided by the sum of the Values of resistors 264 and 270.

When a key is depressed, the change in potential delivers a transitory pulse through trigger capacitor 268 to the base of the trigger transistor 272, which is normally non-conductive and is rendered momentarily conductive by the pulse.

Normally conductive relay transistor 274 is direct coupled to trigger transistor 272, which renders it non-conductive momentarily. The relay coil 276 operates to hold switch 278 normally open, b-ut the contact closes when the coil 276 is de-energized.

The momentary current supply through contact 278 charges capacitor 282 and also lights the control lamp 280, with a timing determined by the RC timing circuit including capacitor 282 and resistor 284. After contact 278 has -opened again, the energy in the capacitor 282 continues the illumination of the light over a decay period determined by the stored energy and the impedance of the lamp 280 itself.

The lamp 280 illuminates the light-sensitive resistor 286, l

which th-us receives illumination of varying intensity, with a time function consisting of a relatively abrupt, timed rise; and an immediate, much slower, timed decay of the logarithmic decrement type.

Means according to the formant control of FIGURE 4 are provided for causing the initial sound to have a predetermined timbre, and to shift to a different timbre at the rate determined by the logarithmic decrement curve of the decay of the lamp280. The lamp 280' performs the function of the knee lever 118 of FIGURE 4, and the lightsensitive resistor 286 corresponds to resistor 180.

Means are provided for terminating this condition in time to let the system respond to the depression of a subsequent key. The charging of capacitor 268 completes itself very quickly, and the pulse that renders transistor 272 conductive ends, and relay transistor 274 becomes conductive again and contact 278 opens. Diode 273 provides a discharge path in series with resistor 270 for rapidly discharging capacitor 268, when the voltage at 266 drops in response to the opening of any key switch 262.

If, now, a second key is depressed while the first key is still held down a second resistor 264 is included in parallel with the rst. It will -be obvious that if the impedance of one resistor 264 is many times greater than that of resistor 270, each additional key closure, up to a substantial number, will cause approximately the same potential change on capacitor 268, and the `transistor 272 can be adjusted to respond to that change, so that any number of keys can be depressed seriatim, at least up to the number of available fingers possessed by the player,

6 and each differently timed closure will trigger the automatic formant action.

'The formant circuit of FIGURE 6 is also useful for developing repeated change from one tone output to another and back again at frequencies higher than can be generated by manual movements, or when manual movement would be tiresome or interfere with other activities by the player. In FIGURE 7 the same light-sensitive resistor 286 receives its illumination through a rotating screen 288 of variable optical density, driven by a motor 290, and the timbre change can follow any desired timed envelope function at any desired frequencies, commonly from about one-half to about sixty cycles per second. At certain appropriate frequencies, this can be made to duplicate the frequencies of activation of the strings of a l plucked stringed instrument or a Xylophone.

In addition, between about 20 and about 60 cycles per second, modulation of timbre or frequency or amplitude produces a gutteral effect closely resembling the acoustic effect produced in brass and other instruments by expert jazz musicians.

In FIGURE 8, I have indicated an organ 300, a preamplifier 304, an amplifier 308, and a loudspeaker 310. Around the preamplifier 304 is a negative feedback circuit 312. A second positive feedback circuit 314 feeds back a signal, the phase ofwhich is a lfunction of frequency; and in a certain frequency range, there is positive feedback which results in emphasizing the harmonics within that range. The frequency-sensitive selective feedback 314 is controlled by the knee lever 118, or equivalent control means. This combination lends itself to use in connection with existing instruments because preampliers with negative feedback to reduce noise and distortion are common.

It is emphasized that the resonant frequency of the formant lters does not alter the effective pitch of the entire signal. It only varies the relative amplitudes of the harmonic components of the received complex signal, so that the wave shape, or timbre, of the delivered signal is changed without noticeable change in frequency.

Others may readily adapt the invention for use under various conditions of service by employing one or more of the novel features disclosed or equivalents thereof.

For instance, the preferred control lever 118 (see FIG- URE 8) is gently and yieldably held in the full-line position by any conventional means such as gravity or a light spring, indicated at 117; and its position of rest may be defined by a stop 119. It will be obvious that an equivalent control member can also be arranged to lie against one side of the players body at the waist or adjacent the axilla, to please the whim of the player or to facilitate playing by someone with a physical handicap. Any of these control members can obviously be arranged to be positively moved in both directions by the player, but a gentle spring pressure toward the stopped position of rest indicated in the drawings is preferred for ordinary usage.

It happens that, on conventional organ consoles, the left foot plays most of the pedal notes and can play them all, leaving the right foot to ride the swell pedal. This anchors the right foot sufficiently to facilitate an accurate and comfortable swinging of the right knee through a distance of two or three inches and the muscular action involved is easily mastered, without disturbing the muscular control of the swell pedal. Another part of the players person available for this control .is the toe of the right foot, which can be swung laterally an inch or so and activate a control member, or carry the swell pedal 101 around with it by rotation about a vertical axis, with the swell pedal pushing the lever.

As at present advised with respect to the apparent scope of my invention, I desire to claim the following subject matter:

1. In an electrical musical instrument, in combination: a signal source; a signal circuit connected to said source to receive the signal therefrom; means for altering said signal circuit to alter the timbre of the signal delivered from said signal circuit; automatic trigger control means for rendering said altering means operative through varying degrees in a predetermined time cycle; and playercontrolled means for activating said source and said trigger means.

2. A combination according to claim 1 in which said signal circuit includes a formant circuit comprising an inductive component and a capacitive component; said formant circuit having a resonant frequency depending on the values of said components; said altering means changing the effective value of one of said components.

3. In an electrical musical instrument, in combination: a signal circuit; a source of audio-frequency signal connected to said signal circuit; a formant circuit operatively associated with said signal circuit for altering the harmonic content of the signal in said circuit; said formant circuit comprising an inductive element and a capacitive element, each having terminals identified as rst and second; said rst terminals being connected to each other and to said signal circuit; an impedance connected between said second terminals; means for impressing at the second terminal of one of said elements a voltage synchronous with said audio-frequency signal for varying the effectiveness of said element, and player-controlled means for varying said synchronous voltage.

4. In an electrical musical instrument, in combination: a signal circuit; a source of audio-frequency signal connected to said signal circuit; a formant circuit operatively associated with said signal circuit for altering the harmonic content of the signal in said circuit; said formant circuit comprising an inductive element and a capacitive element, a connection for delivering signal from said signal circuit to one first terminal of one of said elements; means for delivering to the other, second terminal of said last-mentioned elements, a signal synchronous with the sgnal received by its rst terminal; and player-actuated means for varying the amplitude of said second signal.

5. In an electronic musical instrument, in combination: a plurality of signal sources adapted to deliver signals of predetermined frequencies related to each other in the ratios of small integers; a separate channel circuit for each source; a collector bus bar connected to all said channel circuits to receive signal from them; a light-sensitive resistor in each channel circuit for attenuating the signal in that channel as a function of illumination; a light source adapted to deliver illumination to all said resistors; and player-controlled means for simultaneously varying the relative illumination cf a plurality of said resistors.

References Cited by the Examiner UNITED STATES PATENTS 1,749,685 3/l930 Zouckerman 84-l.2l 2,075,802 4/1937 Davis 84-l.2l 2,562,670 7/1951 Koehl 84-1.l1 2,854,879 10/1958 Anderson i4-1.24 3,039,347 6/1962 Krauss et al SLi- 1.01 3,075,423 1/1963 Brandt et al SLi-1.18

ARTHUR GAUSS, Primary Examiner.

B. P. DAVIS, Assistant Examiner. 

1. IN AN ELECTRICAL MUSICAL INSTRUMENT, IN COMBINATION: A SIGNAL SOURCE; A SIGNAL CIRCUIT CONNECTED TO SAID SOURCE TO RECEIVE THE SIGNAL THEREFROM; MEANS FOR ALTERING SAID SIGNAL CIRCUIT TO ALTER THE TIMBRE OF THE SIGNAL DELIVERED FROM SAID SIGNAL CIRCUIT; AUTOMATIC TRIGGER CONTROL MEANS FOR RENDERING SAID ALTERING MEANS OPERATIVE THROUGH VARYING DEGREES IN A PREDETERMINED TIME CYCLE; AND PLAYERCONTROLLED MEANS FOR ACTIVATING SAID SOURCE AND SAID TRIGGER MEANS. 